1. Field of the Invention
This invention relates to fiber entanglements which resemble cowhide in stiff feeling and exhibit high-degree elongation until structural failure, high resistance to flexural fatigue and high dimensional stability; and, to nonwoven fabrics made therefrom useful as substrates for leather-like sheet materials.
2. Description of the Prior Art
Nonwoven fabrics composed of fiber entanglements have heretofore been used widely as leather-like sheet materials, substrates for leather-like sheet materials, interlining cloths, sanitary materials and sheet materials for industrial use. Furthermore, fiber entanglements are processed into and used as cords or strings. In recent years, several proposals have been made to produce nonwoven fiber entanglement fabrics having improved feeling. Thus, for instance, Japanese Patent Publication No. 18698/81 discloses a method of producing flexible nonwoven fabrics having a cantilever bending resistance of not more than 90 mm which comprises making a web by using a mixture, in a specific proportion, of two polyester fiber species differing in thermal shrinkability, followed by treatment for thermal shrinkage. Japanese Patent Publication No. 59-53388 discloses a method of producing flexible fibrous sheet materials having drapability which comprises making a web from highly shrinkable polyester fibers having latent spontaneous extensibility, subjecting the web to treatment for entanglement, then to treatment for shrinkage and heat-treating the same for spontaneous extension. According to the methods proposed in Japanese Laid Open Patent Publication Nos. 37353/81, 165054/81 and 42952/82, flexible fibrous sheet materials are produced by making a web from a blend of a highly heat-shrinkable fiber and a less heat-shrinkable. fiber, treating the web for entanglement, then for shrinkage and thereafter subjecting the web to heat treatment for spontaneous extension. Furthermore, Japanese Patent Publication No. 37208/85 discloses a method of producing nonwoven fabrics, which closely resemble woven fabrics in performance characteristics, which comprises exposing a web of a highly shrinkable synthetic fiber to a fine high-pressure jet stream of water for entanglement, wet heat treating the web for area shrinkage, drying the same at a temperature at which the form and internal structure of the constituent fibers will not change, and thereafter treating the same for thermal fixation under pressure. The present inventors also disclose fiber entanglement sheet materials made of elastic and nonelastic fibers which are stretchable and improved in feeling and drapability in Japanese Laid Open Patent Publication Nos. 211666/84 and 211664/84 (corresponding to U.S. Pat. No. 4,515,854 and EP No. 125,494).
The prior art fiber entanglement nonwoven fabrics have an increased apparent density of the entanglement as a result of additional shrinkage treatment. However, mere increase in fiber density brings about only a felt-like feeling, which is far from the desired flexible feeling with stiffness or fullness. It is for that reason that it has been proposed to improve the flexibility and drapability by simultaneously blending extensible fibers, performing shrinkage treatment and then carrying out spontaneous extension treatment. Improvements have indeed been made in this way from the feeling viewpoint but, heretofore, fiber entanglement sheet materials have not exhibited the feeling of cowhide which is free from boniness, being a tendency to form wrinkles like miniature ribs when folded, and high crease resistance as well as moderate resilience.
Furthermore, the fiber entanglement sheet materials proposed by the present inventors, which comprise elastic and nonelastic fibers are flexible, exhibit a wide range of stretchability without structural deformation and have good drapability.